The long-term objective of the proposed research is to understand the effects of exercise on the health status of older adults, so as to promote health status and reduce fall-related injuries through carefully designed, safe exercise programs. The specific aims are: (1) to determine and compare the effects of strength training (ST), endurance training (ET), and combined strength/endurance training (ET+ST) on muscle strength, aerobic capacity, gait, balance, functional status, and fall risk; (2) to determine if effects of exercise persist 3 months post-exercise; (3) to gain insight into the mechanism of effects of exercise on functional status; and (4) to identify factors associated with participation in the exercise program. In part, the study hypothesizes that exercise training can produce substantial improvements in health status indicators, and that improvement will correlate with changes in strength. The study is a randomized controlled trial. The major eligibility criteria are age 68-85 and leg weakness at a level associated with impaired health and increased fall risk. Subjects will be recruited from a well-studied group of older adults enrolled in an HMO. By multi-stage screening of about 750 adults, the study plans to randomize 100 persons to one of four groups: ST, ET, ST+ET, and control. A 20% attrition rate is anticipated, giving a final sample size of 80 (10 men and 10 women per group). Exercise sessions of about 1 hour will occur three times/week for 6 months. ST will begin at low levels using arm and ankle weights, then advance to use of a Universal Gym. ET will be bicycle exercise involving both arms and legs. The evaluation design is a repeated measures design with three measurement occasions: pretest, posttest, and follow-up test (at 3 months post- exercise). Strength will be measured at the ankle, knee, hip, elbow, and wrist using an isokinetic dynamometer. Postural sway under different stress conditions will be measured using a force measurement platform. Measures of gait will be made in a gait laboratory using a force platform and a conductive walkway, and include measures of gait events and ground reactive forces. Aerobic capacity at submaximal treadmill and bicycle exercise will be measured. General health status will be measured using validated questionnaire measures. Statistical analysis will use procedures related to repeated measures MANOVA with covariates, such as paired t- tests, and repeated measures ANOVA.